In 2014, airlines in the United States billed more than three billion dollars in “change fees”—fees charged to customers who cancelled or changed itineraries. This bounty came after most of the industry (minus Southwest) tacitly agreed to create a new industry standard of two hundred dollars per change, plus, in some cases, an additional fifty-dollar service fee for tickets booked on non-airline Web sites. And the worst may be yet to come: as the airline-revenue-optimization...